The present invention relates to a process for producing N-substituted formamide, and more in detail, relates to a process for producing N-(.alpha.-hydroxyethyl)formamide and N-(.alpha.-alkoxyethyl)formamide, both of which are important substances as an intermediate for forming useful N-vinylformamide according to the following formulae: ##STR2## wherein R represents an alkyl group.
Hitherto, as a process for producing N-vinylformamide, there have been known a process (1) in which acetaldehydecyanhydrin obtained by reacting acetaldehyde with hydrogen cyanide, as a starting material, is reacted with formamide to form N-(.alpha.-cyanoethyl)formaldehyde and hydrogen cyanide is split off from the obtained N-(.alpha.-cyanoethyl)formamide to obtain the N-vinyl compound, and a process (2) in which N-ethylformamide is reacted with methanol by an electrode reaction to form N-(.alpha.-methoxyethyl)formamide and methanol is split off from the obtained N-(.alpha.-methoxyethyl)formamide to obtain the N-vinyl compound, etc. However, every known process is not an industrially satisfactory method from the viewpoints of the safety of the starting material and of the operation in chemical reaction(s).
Although as a process for obtaining N-(.alpha.-methoxyethyl)formamide, a process in which .alpha.-chloroethyl methyl ether is reacted with formamide in the presence of an excess base has also been known, the process is not practical in factories because of the predominant formation of N,N-di-(.alpha.-methoxyethyl)formamide in the process.
Although the process which uses N-(.alpha.-hydroxyethyl)formamide or a reaction product thereof with an alcohol as the starting material according to the afore-mentioned reaction formula is an industrially advantageous process as compared with the known methods mentioned before, no report has been found on the afore-mentioned process.
Namely, the process for producing N-(.alpha.-hydroxyethyl)formamide wherein formamide which is a primary amide is reacted with acetaldehyde, and the process for producing N-(.alpha.-alkoxy-ethyl)formamide wherein N-(.alpha.-hydroxyethyl)formamide is reacted with a primary or secondary alcohol have not yet been known.
Concerning the reaction between formamide and formaldehyde, various reports have been hitherto published, and in general, N-methylol compound is obtained by the equilibrium reaction of formamide and formaldehyde. In addition, N-methoxymethylamide is formed by the reaction of N-methylolamide with methanol. Accordingly, in the reaction of an aldehyde to formamide, formaldehyde is different from acetaldehyde in its behavior in reaction, namely the reaction of formaldehyde to formamide is substantially different from the reaction of acetaldehyde to formamide.
On the other hand, a process for producing N-(.alpha.-hydroxyethyl)-N-methylformaldehyde by a reaction of a secondary amide such as N-methylformamide and acetaldehyde has been known, for instance, in Japanese Patent Publication No. 45-14283/1970. To be concrete, it is a process for producing N-(.alpha.-hydroxyethyl)-N-alkylamide by reacting a secondary amide with acetaldehyde in the presence of a strongly basic catalyst such as sodium hydroxide or potassium hydroxide or one of the various acid catalysts.
In considering the similarity of the reaction, a use of the catalyst disclosed in the above-mentioned Japanese Patent Publication in the reaction between formamide and acetaldehyde has been examined by the present inventors and as a result, in the case of using a strongly basic catalyst, the yield of N-(.alpha.-hydroxyethyl)formamide did not attain the expected level of practical use, and in the case of using an acid catalyst, N,N'-ethylidene-bisformamide was formed without producing the object compound.
As has been described, the reaction conditions for industrial production of N-(.alpha.-hydroxyethyl)formamide by the reaction between formamide and acetaldehyde are to be selected by the viewpoint quite different from the reaction between formamide and formaldehyde or from the reaction between a secondary amide and acetaldehyde.
The object of the present invention is to provide an industrially profitable process for producing N-(.alpha.-hydroxyethyl)formamide and N-(.alpha.-alkoxyethyl)formamide as an intermediate raw material for N-vinylformamide, and such an object is easily attained by reacting formamide with acetaldehyde in the presence of a basic catalyst and, if required, by further reacting the reaction product with a primary or secondary alcohol in the presence of an acid catalyst.
The N-substituted formamide obtained according to the present invention is represented by the formula (I): ##STR3## wherein R represents a hydrogen atom or a residual radical of a primary or secondary alcohol, and N-vinylformamide is obtained by thermally decomposing the N-substituted formamide represented by the formula (I).